The gain control circuit of the wireless receiver is used for achieving the purpose of high dynamic range; accordingly, the amplifier gain can be altered depending on the magnitude of the input signal. Therefore, while the magnitude of the input signal is small, the gain control circuit will be with high gain amplified the input signal, otherwise, while the magnitude of the input signal is large, the gain control circuit will be with low gain amplified the input signal, thereby, it is advantageously for demodulating by the further demodulator.
The analog gain controlling process or digital gain controlling process is selectively used for regulating the gain of each stage amplifier according to the prior art, wherein the analog gain control circuit can be applied to switch the gain of the amplifier slowly for reducing the transient response, thereby, the affect with respect to the quality of the input signal can be prevented.
Nevertheless, the RF specification of each stage amplifier has to be considered for each other during the gain regulation for preventing the error occurred while the analog gain controlling process is applied, therefore, according to the amplifier being with the exact RF specification, such as low noise amplifier (LNA), the amplifier will be easily to operate within the non-linear area while the gain thereof is regulating by the analog gain controlling process, such that the gain of the input signal will not achieve the requirement of the linearity, accordingly, the wireless receiver cannot be operated optimally.
The digital gain control circuit is used for improving the gain linear of the amplifier. In detail, the gain of each stage amplifier can be regulated respectively according to the RF specification thereof, as well as, the consideration for the RF specification of each stage amplifier is unnecessary during the gain regulation, thereby, the wireless receiver will be with better linear accordingly.
However, since the requirement of the gain magnitude can be reached at once by the digital gain controlling process, the input signal will be with transient response occurred intensely while the gain magnitude is increased or decreased substantially, therefore, the difficulty of the input signal demodulation will be increased due to the input signal has been effected by the transient response. That is, there are still defects on the analog gain controlling process and digital gain controlling process for regulating the gain of each stage amplifier surely.